The invention relates to a dynamic pressure bearing having a mechanism for preventing liquid lubricant from leaking.
FIG. 4 shows such a type of dynamic pressure bearing of the conventional art. The dynamic pressure bearing has a dynamic pressure bearing portion 83 which is formed between a housing 81 and a shaft 82. A capillary seal 85 is formed in an opening end of the housing 81. The capillary seal 85 is configured by a tapered shaft portion 86, and an inner peripheral face 87 of the housing 81 which is opposed to the portion. The inner peripheral face 87 is configured by: a tapered portion 88 in which the diameter is gradually reduced as moving from the opening toward the inner area in the axial direction; and a straight portion 89 which is continuous at a constant diameter to the bearing portion 83.
In the capillary seal 85, the clearance between the shaft 82 and the housing 81 is gradually reduced as moving toward the inner area in the axial direction. Therefore, liquid lubricant is sucked by capillary action into the side of the bearing portion 83, thereby preventing the lubricant from leaking.
When the rotation center axis of the housing 81 revolves about the center axis of the shaft 82 or the housing performs whirling movement (precession movement), a centrifugal force acts in a direction along which the liquid lubricant is discharged to the outside of the bearing portion 83. This produces a problem in that, when the centrifugal force exceeds the capillary effect of the capillary seal 85, the liquid lubricant leaks out from the opening of the housing 81.
Therefore, it is an object of the invention to provide a dynamic pressure bearing in which leakage of liquid lubricant due to precession of a housing can be prevented from occurring.
In order to attain the object, the dynamic pressure bearing of the invention of claim 1 is a dynamic pressure bearing in which a shaft is inserted into a housing, and dynamic pressure grooves are formed in at least one of a bearing portion of the housing and an outer peripheral face of the shaft, wherein
the shaft has a tapered shaft portion which is adjacent to the bearing portion, and in which a diameter is gradually reduced as moving toward an opening of the housing, the housing has a tapered inner peripheral face which is opposed to the tapered shaft portion, and in which an inner diameter is gradually increased as moving from the opening toward an inner area in an axial direction,
the tapered shaft portion and the tapered inner peripheral face constitute a capillary sealing portion, and
a clearance between the tapered shaft portion and the tapered inner peripheral face is gradually reduced as moving from the opening toward the inner area in the axial direction.
In the dynamic pressure bearing of the invention, the inner diameter of the tapered inner peripheral face of the housing which constitutes the capillary sealing portion is gradually increased as moving from the opening toward the inner area in the axial direction. When the housing is rotated, therefore, a centrifugal force applied on liquid lubricant existing on the tapered inner peripheral face acts in the direction along which the liquid lubricant is pushed toward the inner area. Consequently, the centrifugal force which is due to precession of the housing, and which pushes the liquid lubricant toward the outside can be cancelled by the force acting in the direction along which the liquid lubricant is pushed toward the inner area, with the result that leakage of the liquid lubricant due to precession of the housing can be prevented from occurring.